7471a

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CD-ROM 7471A - 1 Revision 1September 1994

METHOD 7471A

MERCURY IN SOLID OR SEMISOLID WASTE (MANUAL COLD-VAPOR TECHNIQUE)

1.0 SCOPE AND APPLICATION

1.1 Method 7471 is approved for measuring total mercury (organic andinorganic) in soils, sediments, bottom deposits, and sludge-type materials. All

samples must be subjected to an appropriate dissolution step prior to analysis.If this dissolution procedure is not sufficient to dissolve a specific matrixtype or sample, then this method is not applicable for that matrix.

2.0 SUMMARY OF METHOD

2.1 Prior to analysis, the solid or semi-solid samples must be preparedaccording to the procedures discussed in this method.

2.2 Method 7471, a cold-vapor atomic absorption method, is based on theabsorption of radiation at the 253.7-nm wavelength by mercury vapor. The mercuryis reduced to the elemental state and aerated from solution in a closed system.The mercury vapor passes through a cell positioned in the light path of an atomic

absorption spectrophotometer. Absorbance (peak height) is measured as a functionof mercury concentration.

2.3 The typical instrument detection limit (IDL) for this method is0.0002 mg/L.

3.0 INTERFERENCES

3.1 Potassium permanganate is added to eliminate possible interferencefrom sulfide. Concentrations as high as 20 mg/Kg of sulfide, as sodium sulfide,do not interfere with the recovery of added inorganic mercury in reagent water.

3.2 Copper has also been reported to interfere; however, copper concen-trations as high as 10 mg/Kg had no effect on recovery of mercury from spikedsamples.

3.3 Samples high in chlorides require additional permanganate (as muchas 25 mL) because, during the oxidation step, chlorides are converted to freechlorine, which also absorbs radiation of 253 nm. Care must therefore be takento ensure that free chlorine is absent before the mercury is reduced and sweptinto the cell. This may be accomplished by using an excess of hydroxylaminesulfate reagent (25 mL). In addition, the dead air space in the BOD bottle mustbe purged before adding stannous sulfate.

3.4 Certain volatile organic materials that absorb at this wavelength may

also cause interference. A preliminary run without reagents should determine ifthis type of interference is present.4.0 APPARATUS AND MATERIALS

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4.1 Atomic absorption spectrophotometer or equivalent: Any atomicabsorption unit with an open sample presentation area in which to mount theabsorption cell is suitable. Instrument settings recommended by the particularmanufacturer should be followed. Instruments designed specifically for themeasurement of mercury using the cold-vapor technique are commercially availableand may be substituted for the atomic absorption spectrophotometer.

4.2 Mercury hollow cathode lamp or electrodeless discharge lamp.

4.3 Recorder: Any multirange variable-speed recorder that is compatiblewith the UV detection system is suitable.

4.4 Absorption cell: Standard spectrophotometer cells 10 cm long withquartz end windows may be used. Suitable cells may be constructed from Plexiglastubing, 1 in. O.D. x 4.5 in. The ends are ground perpendicular to thelongitudinal axis, and quartz windows (1 in. diameter x 1/16 in. thickness) arecemented in place. The cell is strapped to a burner for support and aligned inthe light beam by use of two 2-in. x 2-in. cards. One-in.-diameter holes are cutin the middle of each card. The cards are then placed over each end of the cell.The cell is then positioned and adjusted vertically and horizontally to give themaximum transmittance.

4.5 Air pump: Any peristaltic pump capable of delivering 1 L/min air maybe used. A Masterflex pump with electronic speed control has been found to besatisfactory.

4.6 Flowmeter: Capable of measuring an air flow of 1 L/min.

4.7 Aeration tubing: A straight glass frit with a coarse porosity. Tygontubing is used for passage of the mercury vapor from the sample bottle to theabsorption cell and return.

4.8 Drying tube: 6-in. x 3/4-in.-diameter tube containing 20 g ofmagnesium perchlorate or a small reading lamp with 60-W bulb which may be used

to prevent condensation of moisture inside the cell. The lamp should bepositioned to shine on the absorption cell so that the air temperature in thecell is about 10 C above ambient.o

4.9 The cold-vapor generator is assembled as shown in Figure 1 of

reference 1 or according to the instrument manufacturers instructions. Theapparatus shown in Figure 1 is a closed system. An open system, where themercury vapor is passed through the absorption cell only once, may be usedinstead of the closed system. Because mercury vapor is toxic, precaution must betaken to avoid its inhalation. Therefore, a bypass has been included in thesystem either to vent the mercury vapor into an exhaust hood or to pass thevapor through some absorbing medium, such as:

1. equal volumes of 0.1 M KMnO and 10% H SO , or4 2 42. 0.25% iodine in a 3% KI solution.

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A specially treated charcoal that will adsorb mercury vapor is alsoavailable from Barneby and Cheney, East 8th Avenue and North CassidyStreet, Columbus, Ohio 43219, Cat. #580-13 or #580-22.

4.10 Hot plate or equivalent - Adjustable and capable of maintaining atemperature of 90-95 C.o

4.11 Graduated cylinder or equivalent.

5.0 REAGENTS

5.1 Reagent Water: Reagent water will be interference free. Allreferences to water in this method refer to reagent water unless otherwisespecified.

5.2 Aqua regia: Prepare immediately before use by carefully adding threevolumes of concentrated HCl to one volume of concentrated HNO .3

5.3 Sulfuric acid, 0.5 N: Dilute 14.0 mL of concentrated sulfuric acidto 1 liter.

5.4 Stannous sulfate: Add 25 g stannous sulfate to 250 mL of 0.5 N

sulfuric acid. This mixture is a suspension and should be stirred continuouslyduring use. A 10% solution of stannous chloride can be substituted for stannoussulfate.

5.5 Sodium chloride-hydroxylamine sulfate solution: Dissolve 12 g ofsodium chloride and 12 g of hydroxylamine sulfate in reagent water and dilute to100 mL. Hydroxylamine hydrochloride may be used in place of hydroxylaminesulfate.

5.6 Potassium permanganate, mercury-free, 5% solution (w/v): Dissolve5 g of potassium permanganate in 100 mL of reagent water.

5.7 Mercury stock solution: Dissolve 0.1354 g of mercuric chloride in75 mL of reagent water. Add 10 mL of concentrated nitric acid and adjust thevolume to 100.0 mL (1.0 mL = 1.0 mg Hg).

5.8 Mercury working standard: Make successive dilutions of the stockmercury solution to obtain a working standard containing 0.1 ug/mL. This workingstandard and the dilution of the stock mercury solutions should be prepared freshdaily. Acidity of the working standard should be maintained at 0.15% nitricacid. This acid should be added to the flask, as needed, before adding thealiquot.6.0 SAMPLE COLLECTION, PRESERVATION, AND HANDLING

6.1 All samples must have been collected using a sampling plan thataddresses the considerations discussed in Chapter Nine of this manual.

6.2 All sample containers must be prewashed with detergents, acids, andreagent water. Plastic and glass containers are both suitable.

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6.3 Non-aqueous samples shall be refrigerated, when possible, andanalyzed as soon as possible."

7.0 PROCEDURE

7.1 Sample preparation: Weigh triplicate 0.2-g portions of untreatedsample and place in the bottom of a BOD bottle. Add 5 mL of reagent water and5 mL of aqua regia. Heat 2 min in a water bath at 95 C. Cool; then add 50 mLo

reagent water and 15 mL potassium permanganate solution to each sample bottle.Mix thoroughly and place in the water bath for 30 min at 95 C. Cool and add 6o

mL of sodium chloride-hydroxylamine sulfate to reduce the excess permanganate.

CAUTION: Do this addition under a hood, as Cl could be evolved.2Add 55 mL of reagent water. Treating each bottle individually, add5 mL of stannous sulfate and immediately attach the bottle to theaeration apparatus. Continue as described under step 7.4.

7.2 An alternate digestion procedure employing an autoclave may also beused. In this method, 5 mL of concentrated H SO2 4 3and 2 mL of concentrated HNOare added to the 0.2 g of sample. Add 5 mL of saturated KMnO solution and cover4the bottle with a piece of aluminum foil. The samples are autoclaved at 121 Co

and 15 lb for 15 min. Cool, dilute to a volume of 100 mL with reagent water, andadd 6 mL of sodium chloride-hydroxylamine sulfate solution to reduce the excesspermanganate. Purge the dead air space and continue as described under step 7.4.Refer to the caution statement in section 7.1 for the proper protocol in reducingthe excess permanganate solution and adding stannous sulfate.

7.3 Standard preparation: Transfer 0.0-, 0.5-, 1.0-, 2.0-, 5.0-, and 10-mL aliquots of the mercury working standard, containing 0-1.0 ug of mercury, toa series of 300-mL BOD bottles or equivalent. Add enough reagent water to eachbottle to make a total volume of 10 mL. Add 5 mL of aqua regia and heat 2 minin a water bath at 95 C. Allow the sample to cool; add 50 mL reagent water ando

15 mL of KMnO solution to each bottle and return to the water bath for 304

min. Cool and add 6 mL of sodium chloride-hydroxylamine sulfate solution toreduce the excess permanganate. Add 50 mL of reagent water. Treating eachbottle individually, add 5 mL of stannous sulfate solution, immediately attachthe bottle to the aeration apparatus, and continue as described inStep 7.4.

7.4 Analysis: At this point, the sample is allowed to stand quietlywithout manual agitation. The circulating pump, which has previously beenadjusted to a rate of 1 L/min, is allowed to run continuously. The absorbance,as exhibited either on the spectrophotometer or the recorder, will increase andreach maximum within 30 sec. As soon as the recorder pen levels off(approximately 1 min), open the bypass valve and continue the aeration until theabsorbance returns to its minimum value. Close the bypass valve, remove the

fritted tubing from the BOD bottle, and continue the aeration.

7.5 Construct a calibration curve by plotting the absorbances of stan-dards versus micrograms of mercury. Determine the peak height of the unknownfrom the chart and read the mercury value from the standard curve. Duplicates,spiked samples, and check standards should be routinely analyzed.

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7.6 Calculate metal concentrations: (1) by the method of standard

additions, (2) from a calibration curve, or (3) directly from the instrument'sconcentration read-out. All dilution or concentration factors must be taken intoaccount. Concentrations reported for multiphased or wet samples must beappropriately qualified (e.g., 5 ug/g dry weight).8.0 QUALITY CONTROL

8.1 Refer to section 8.0 of Method 7000.

9.0 METHOD PERFORMANCE

9.1 Precision and accuracy data are available in Method 245.5 of Methodsfor Chemical Analysis of Water and Wastes.

9.2 The data shown in Table 1 were obtained from records of state andcontractor laboratories. The data are intended to show the precision of thecombined sample preparation and analysis method.

10.0 REFERENCES

1. Methods for Chemical Analysis of Water and Wastes, EPA-600/4-82-055,December 1982, Method 245.5.

2. Gaskill, A., Compilation and Evaluation of RCRA Method Performance Data,Work Assignment No. 2, EPA Contract No. 68-01-7075, September 1986.

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TABLE 1. METHOD PERFORMANCE DATA

Sample Preparation LaboratoryMatrix Method Replicates

Emission control dust Not known 12, 12 ug/g

Wastewater treatment sludge Not known 0.4, 0.28 ug/g

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METHOD 7471AMERCURY IN SOLID OR SEMISOLID WASTE (MANUAL COLD-VAPOR TECHNIQUE)

7471a

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